For me the best buildings in Edinburgh are:
Distillers Building by RMJM on Belmont Road Murray Field
Scottish Provident Building by Rowand Anderson on St Andrews Square across the square is a building by Basil Spence;
Mortonhall cremetorium by Basil Spence
All first class buildings and all the best examples of modern architecture Auld Reekie has to offer.
Of the new stuff, the Mirrales's Parliament looks very good although covered in scaffold but you can see emerging a very interesting building and the masterplannig of the area
around by John Hope is innovative.
You could have a look inside the new museum of Scotland I guess, if your running for your train.
Don't though try to see to much though, just enjoy the day. Edinburgh is beautiful, probably one of the most beautiful city's on the planet.